Abstract: In this paper, the kernel function method was introduced into the concentration calculation of the random walk model to replace the box method. And a change to the bandwidth of the kernel function was proposed to form a frequency bandwidth kernel function by relating it to convection diffusion time. By comparing the calculated concentration of analytical solution with the fixed bandwidth Gaussian kernel function, the fixed bandwidth Epanechnikov kernel function, the frequency bandwidth Gaussian kernel function, the frequency bandwidth Epanevhnikov kernel function and the box method, the conclusion was obtained that the frequency bandwidth Epanevhnikov kernel function can efficiently improve the accuracy of the contaminated concentration calculation without increasing simulated particles.